Loudspeaker System with Improved Sound

ABSTRACT

A loudspeaker device is presented which includes a zeolite material comprising zeolite particles having a silicon to aluminum mass ratio of at least 200. For an increased pore fraction of pores with a diameter in a range between 0.7 micrometer and 30 micrometer shows an increased shift of the resonance frequency down to lower frequencies has been observed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/818,374, filed Feb. 23, 2013, which is a national stage ofPCT/IB2011/053685, filed Aug. 23, 2011, which claims priority toEuropean Patent Application No. 10173765.8 filed Aug. 23, 2010, thedisclosures of which are incorporated in their entirety by referenceherein.

FIELD OF INVENTION

The present invention relates to the field of loudspeaker devices.

ART BACKGROUND

In loudspeaker devices, including a loudspeaker, a housing and aresonance space, gas adsorbing materials—in the following referred to assorber—like e.g. activated carbon or zeolite may be placed therein toimprove sound generation of the loudspeaker device. A sorber in theresonance space of the loudspeaker leads to an apparent virtualenlargement of the resonance space by gas adsorption and desorption. Theresonance frequency of the loudspeaker device is thereby lowered to avalue that can be achieved without sorber only with an essentiallylarger resonance space.

However, it turned out that the use of sorbers bears several problems.One problem is the aging of the sorber in particular by irreversibleadsorption of substances with high vapour pressure.

EP 2 003 924 A1 relates to a loudspeaker system in which a gas adsorber,obtained by adding a binder to a porous material including a pluralityof grains so as to perform moulding, is used to physically adsorb a gasin a closed space of the speaker system. The porous material may be madeof one selected from the group consisting of an activated carbon,zeolite, silica (SiO₂), alumina (Al₂O₃), zirconia (ZrO₃), magnesia(MgO), iron oxide black (Fe₃O₄) molecular sieve, fullerene and a carbonnanotube. The binder may be one of a powdery resin material and afibrous resin material.

In view of the above-described situation, there exists a need for animproved technique that enables to increase the virtual acoustic volumeof a resonance space of a loudspeaker device while substantiallyavoiding or at least reducing one or more of the above-identifiedproblems.

SUMMARY OF THE INVENTION

This need may be met by the subject matter according to the independentclaims. Advantageous embodiments of the herein disclosed subject matterare described by the dependent claims.

According to a first aspect of the invention there is providedloudspeaker device comprising a loudspeaker receptacle for receiving aloudspeaker, and a zeolite material comprising zeolite particles havinga silicon to aluminum mass ratio of at least 200. According toembodiments, the zeolite material comprises zeolite particles in pureSiO₂ modification. It should be noted that herein the term “silicon toaluminum mass ratio of at least 200” includes higher silicon to aluminummass ratios, e.g. 250 or 300, as well as aluminum-free zeoliteparticles. In the latter case, the whole zeolite particles of thezeolite material are in pure SiO₂ modification.

The experiments performed by the inventors showed that such zeoliteparticles may provide a good sorption capacity per volume unit and aslow aging behavior. Zeolites are microporous minerals, usuallyaluminosilicate minerals, and are known to a person skilled in the art.Basic information about zeolites is available from the InternationalZeolite Association and the corresponding web site(http://www.iza-online.org/).

Generally herein a loudspeaker refers to any type of electro-acoustictransducer.

According to an embodiment of the first aspect, at least part of thezeolite particles have the structure FER. According to a furtherembodiment, at least part of the zeolite particles have the structureMFI. According to an embodiment, all of the zeolite particles are of thesame structure, e.g. the structure FER. According to other embodiments,the zeolite material includes zeolite particles of at least twodifferent structures. For example, in an embodiment, the zeolitematerial includes zeolite particles of the structure FER and zeoliteparticles of the structure MFI. Herein the three letter code relates tothe classification of zeolites according to the International ZeoliteAssociation and can be obtained inter alia fromhttp://www.iza-online.org/.

According to a further embodiment, the zeolite material furthercomprises a binder adhering the individual zeolite particles together.This allows grains of zeolite material to be formed which are largerthan a single zeolite particle. Further a certain spacing betweenzeolite particles can be established by the binder and appropriateprocessing of the ingredients of the zeolite material.

According to a further embodiment, the zeolite particles comprise firstpores having a diameter in a first diameter range and the zeolitematerial comprises second pores between different zeolite particles. Thesize of first pores in the zeolite particles usually have a sharp porediameter distribution. The diameter of the second pores can beinfluenced by the manufacturing process of the zeolite material.

According to an embodiment, the second pores have a diameter in a seconddiameter range and the second diameter range is spaced from the firstdiameter range by at least one order of magnitude. For example, if thefirst diameter range extends up to about 4 nanometers, according to anembodiment the second diameter range of the second pores extends fromabout 40 nanometers to higher diameters.

According to a further embodiment, the second pores have a pore diameterlarger than 50 nanometer.

According to a still further embodiment, the zeolite material has secondpores in the range between 0.7 micrometer and 30 micrometer. Accordingto a further embodiment, the zeolite material has second pores in therange between 1 micrometer and 10 micrometer.

According to an embodiment of the first aspect, the second pores have apore diameter distribution with a local peak in a diameter range between0.7 micrometer and 30 micrometer. According to an further embodiment,the second pores have a pore diameter distribution with a local peak ina diameter range between 1 micrometer and 10 micrometer.

According to a further embodiment, the zeolite material comprises grainshaving a plurality of the zeolite particles adhered together with thebinder and the grains have an average grain size in a range between 0.2millimeter and 0.9 millimeter.

According to a further embodiment, in relation to the whole mass of thezeolite material the mass fraction of the binder is in the range from 1%to 20%. According to a further embodiment, in relation to the whole massof the zeolite material the mass fraction of the binder is in the rangefrom 2% to 10%. According to a further embodiment, in relation to thewhole mass of the zeolite material the mass fraction of the binder is inthe range from 4% to 6%.

According to an embodiment, the zeolite particles have a mean diameterbelow 10 micrometer. According to a further embodiment, the zeoliteparticles have a mean diameter below 5 micrometer. According to afurther embodiment, the zeolite particles have a mean diameter below 2micrometer.

According to an embodiment, the zeolite particles have a mean diameterabove 0.1 micrometer. According to a further embodiment, the zeoliteparticles have a mean diameter above 0.3 micrometer, or, according tostill other embodiments, above 0.5 micrometer.

According to a second aspect, a zeolite material is provided, thezeolite material being obtainable by: (i) preparing a zeolite suspensionfrom zeolite particles having a silicon to aluminum mass ratio of atleast 200 and an nonpolar solvent; (ii) mixing the zeolite suspensionwith a binder suspension to obtain a zeolite-binder mixture; and (iii)drying the zeolite-binder mixture. According to embodiments of thesecond aspect, the zeolite material is configured or processed asdescribed with regard to the first aspect or embodiments and examplesthereof.

According to embodiments of the herein disclosed subject matter, azeolite material is obtained by (a) preparing a zeolite suspension withan organic solvent, e.g. alcohol, wherein the zeolite particles have amean particle diameter smaller than 10 micrometer or, according toanother embodiment, smaller than 2 micrometer. (b) The zeolitesuspension is homogenized, e.g. by stirring. (c) The homogenized zeolitesuspension is mixed with a binder suspension, e.g. a latex suspension.Embodiments of Latex suspensions include at least one of a Polyacrylatesuspension, Polystyrolacetat suspension, Polyvinylacetat suspension,Polyethylvinylacetat suspension, Polybutadienrubber suspension, etc.According to an embodiment, the mass concentration of the binder, e.g.the polymer, is between 1 weight % and 10 weight %, or, according otherembodiments, between 4 weight % and 6 weight %. The resultant suspensionis then dried. Drying can be performed in different ways, e.g. by meansof a fluidized bed, a spray method or by pouring the resultantsuspension onto a hot plate (according to embodiments the temperature ofthe plate is in a range between 120 degrees Celsius and 200 degreesCelsius or between 150 degrees Celsius and 170 degrees Celsius). If thegrains of the resultant solid are larger than desired, the resultantsolid may be cut or broken into smaller pieces e.g. by means of a mortarmill, a hammer rotor mill, a cutting mill or a oscillating plate mill.(d) Subsequently, the resultant solid (optionally cut or broken) isscreened with sieves to obtain grains in a desired diameter range.

According to a third aspect, a method of producing a zeolite materialfor use as a sorber material in loudspeaker device is provided, themethod comprising (i) preparing a zeolite suspension from zeoliteparticles having a silicon to aluminum mass ratio of at least 200 and asolvent that includes an organic solvent; (ii) mixing the zeolitesuspension with a binder suspension to obtain a zeolite-binder mixture;and (iii) drying the zeolite-binder mixture. According to embodiments ofthe third aspect, the zeolite material is configured or processed asdescribed with regard to the first aspect or embodiments and examplesthereof.

According to an embodiment, the solvent consists of at least one organicsolvent. According to a further embodiment, the solvent comprises atleast one organic solvent and at least one inorganic solvent.

According to a fourth aspect, there is provided a use of a zeolitematerial having zeolite particles with a silicon to aluminum mass ratioof at least 200 in a loudspeaker device region that is exposed to soundgenerated by a loudspeaker of the loudspeaker device. According toembodiments of the fourth aspect, the zeolite material is configured orprocessed as described with regard to the first aspect or embodimentsand examples thereof.

In the above there have been described and in the following there willbe described exemplary embodiments of the subject matter disclosedherein with reference to a loudspeaker device, a zeolite material, amethod of producing a zeolite material and a use of a zeolite material.It has to be pointed out that of course any combination of featuresrelating to different aspects of the herein disclosed subject matter isalso possible. For example, some embodiments have been described withreference to apparatus type claims whereas other embodiments have beendescribed with reference to method type claims. However, a personskilled in the art will gather from the above and the followingdescription that, unless otherwise notified, in addition to anycombination of features belonging to one aspect also any combinationbetween features relating to different aspects or embodiments, forexample even between features of the apparatus type claims and featuresof the method type claims, is considered to be disclosed with thisapplication.

The aspects and embodiments defined above and further aspects andembodiments of the present invention are apparent from the examples tobe described hereinafter and are explained with reference to thedrawings, but to which the invention is not limited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a measurement circuit for impedancemeasurements.

FIG. 2 schematically shows a measurement circuit for measuring theimpedance response of a loudspeaker device.

FIG. 3 schematically shows a measurement circuit for sound pressurelevel measurements.

FIG. 4 schematically shows a grain of a zeolite material in accordancewith embodiments of the herein disclosed subject matter.

FIG. 5 schematically shows a zeolite material in accordance withembodiments of the herein disclosed subject matter.

FIG. 6 shows nitrogen adsorption isotherms for zeolites in accordancewith embodiments of the herein disclosed subject matter.

FIG. 7 shows nitrogen adsorption isotherms for BEA zeolites before andafter aging.

FIG. 8 shows nitrogen adsorption isotherms for MFI zeolites before andafter aging.

FIG. 9 shows nitrogen adsorption isotherms for FER zeolites before andafter aging.

FIG. 10 shows electrical impedance curves for zeolites in accordancewith embodiments of the herein disclosed subject matter.

FIG. 11 shows cumulative pore volume curves for zeolites in accordancewith embodiments of the herein disclosed subject matter.

FIG. 12 shows electrical impedance curves for zeolite materials of FIG.11 and for an empty resonance space.

FIG. 13 shows sound pressure level measurements for a loudspeaker devicein accordance with embodiments of the herein disclosed subject matter,for a loudspeaker device with empty resonance space and for aloudspeaker device having activated carbon fibers in its resonancespace.

FIG. 14 shows electrical impedance curves for different grain sizes ofzeolite material in accordance with embodiments of the herein disclosedsubject matter.

FIG. 15 shows electrical impedance curves for zeolite materials withdifferent polymer content in accordance with embodiments of the hereindisclosed subject matter.

FIG. 16 shows a loudspeaker device in accordance with embodiments of theherein disclosed subject matter.

DETAILED DESCRIPTION

The illustration in the drawings is schematic. It is noted that indifferent figures, similar or identical elements are provided with thesame reference signs or with reference signs, which are different fromthe corresponding reference signs only within the first digit.

In the following, the measurement methods employed to determine theexperimental results which are presented herein are described.

Room Temperature Nitrogen Sorption Measurements

Nitrogen adsorption isotherms have been determined at 25 degrees Celsius(° C.) between 25 millibar (mbar) and 1100 mbar with a sorptionmeasurement device “Nova 1000e” of the firm “Quantachrome”. Furthertechnical information is available from the technical datasheets of thefirm “Quantachrome”, e.g. in the section “A Method for the Determinationof Ambient Temperature Adsorption of Gases on Porous Materials” inPowder Tech Note 19.

Measurement of the Electrical Impedance

The measurement of the loudspeaker impedance is based on the circuit 30shown in FIG. 1. A reference resistance R2 is connected between anexciting signal source 2 and a loudspeaker 3. R1 denotes the ohmicresistance of the supply lines 1.

The electrical impedance is frequency dependent. After measurement ofthe voltages U1 and U2 as a function of frequency f, i.e. U1(f) andU2(f), the impedance Z is calculated according to the followingequation:

${Z(f)} = {\frac{U\; 2(f)}{{U\; 2(f)} - {U\; 1(f)}}R\; 2}$

The measurement circuit 40 for determining the impedance response shownin FIG. 2 comprises a loudspeaker of the type NXP RA11×15×3.5, serialNo. 0001A5 9205E 11141345, indicated at 3 in FIG. 2, which has beenmounted hermetically sealed with a sealing 4 over a closed volume 5 (ca.500 mm³, 12.5 mm×9.5 mm×4.2 mm). The closed volume 5 forms a resonancespace for the loudspeaker. The resonance frequency with the resonancespace being empty is 1000 Hz. In an exemplary embodiment, the excitingsignal was generated by a computer soundcard 7 wherein the excitingsignal is provided to the loudspeaker via an audio output port 6 of thecomputer soundcard 7. The left line output port 6 serves to output thetest signal, the left line input port 8 serves for acquisition of adevice under test (DUT) signal and the right line input port 9 serves asa reference input port. The resistance 10 serves for damping the testsignal.

By a resonance effect there is generated an amplification of the testsignal, wherein the amplification depends on the volume of the resonancespace. If the volume of the resonance space is empty, there is a certainamplification of the test signal at a certain frequency. By reducing thevolume, the amplification shifts towards higher frequencies. Byenlargement of the volume or by placing a suitable zeolite material inthe resonance space the maximum of the amplification can be shifted tolower frequencies.

Sound Pressure Level Measurements

FIG. 3 schematically shows the experimental setup 50 for the soundpressure level measurements. The left output port 11 of the soundcard 12is used as a signal source for the loudspeaker 3. The left input 14 ofthe soundcard is used for recording the output voltage of a microphone15.

For evaluation of the measurement data the programs “Arta” and “Limp”have been used. Further details on the evaluation and the experimentalsetup can be taken from the users guide of the programs “Arta” and“Limp”. The users guides are available underhttp://www.fesb.hr/˜mateljan/arta/.

Results and Description of Embodiments

According to the findings of the inventors, the prior art does notprovide a loudspeaker system with an aging resistant, well functioningadsorber with a low acoustic resistance. For example, activated carboncan be used as gas adsorbing material, however there are a plurality ofproblems. Activated carbon is electrically conducting and can interferewith the electromagnetic transducers of the loudspeaker or otherelectronic parts within or external to the loudspeakers. Interactionwith the surrounding equipment generated by induction of currents in theelectrically conducting material are usually undesirable. For example,if an antenna is placed close to the electrically conducting material,the transmit power of the antenna is reduced.

Further, the use of carbon-based materials can lead to further problems.For example, it has been observed by the inventors that the chemicallyreactive activated carbon can react with metal parts of the loudspeakerhousing leading to corrosion. Another severe problem with the use ofactivated carbon is the occurrence of short circuits by aberration ofthe activated carbon.

No electrically non-conducting sorption material is known which resultsin a virtual acoustic enlargement of the volume of the resonance spaceby at least a factor of 2 for resonance frequencies of larger 500 Hz. Byan enlargement of the virtual acoustic volume by the factor of 2,resonance shifts to lower frequencies of over 150 Hz can be achievedwith known miniature loudspeaker systems. For achieving a high virtualenlargement of the resonance space a high sorption capacity for nitrogenas a main portion of air and a high sorption coefficient (dn/dp) at 10⁵Pa is important in order to allow a large volume of gas to adsorb on ordesorb from the sorption material when pressure variations occur. Herein“n” denotes the adsorbed amount of gas and “p” denotes the pressure ofthe gas.

For a good sorption capacity the surface of the sorber should be aslarge as possible since the gas molecules adsorb primarily on thesurface. However, other parameters such as morphology, chemicalstructure, curvature of the surface, etc. is important for the sorptioncapacity of the material. However, an exact correlation between theabove properties of a substance and its sorption properties is unknown,at least for gases at temperatures above their critical temperature Tc.This is the case for Oxygen and Nitrogen at ambient temperature, sinceTc(N₂)=126 K and Tc(O₂)=155 K. Since the volume that is available forthe sorber is limited, a criterion for suitability of the sorber forvirtual acoustic volume enlargement is the sorption capacity per volumeunit. Hence, the sorption capacity per mass unit are only of limitedinterest.

According to the findings of the inventors, a sorber with intrinsicallynon-porous material and low particle size is unsuitable for achieving avirtual acoustic enlargement of a resonance space. Such a material isdried colloidal SiO₂ with a particle size of about 9 nm. For such aparticle size, the binder particles should be of the same size becauseotherwise the amount of sorber particles per volume unit and hence theadsorbing surface per volume unit would decrease to a large extent.However, a distance between sorber particles in nanometer range resultsin an undesired high acoustic resistance for the sorber.

For materials with a large internal surface, i.e. for intrinsicallyporous materials such as zeolites, larger particles can be used forbuilding the sorber.

Zeolites are typically synthesized in particle sizes up to 10 μm. Ifthese particles are glued to each other in a simple manner, theresulting acoustic resistance is too high due to low distances betweenthe particles.

One problem with zeolite particles with a diameter over 10 μm is theaccessibility of the inner regions of these particles. Since the timespan for the respective adsorption and desorption process is within afew milliseconds, the path to the adsorption location should be as shortas possible which is not realized for particles greater 10 μm. Hence, incomparison to smaller particles there is only a limited increase of thevirtual acoustic volume of the resonance space filled with suchparticles.

FIG. 4 shows a zeolite material 100 in accordance with embodiments ofthe herein disclosed subject matter. The zeolite material 100 compriseszeolite particles, some of which are denoted by 102 in FIG. 4. Thezeolite particles have internal, first pores 104, indicated by thestructure shown within the individual zeolite particles shown in FIG. 4.

The zeolite particles are adhered together with a binder (not shown inFIG. 4). In accordance with an embodiment of the herein disclosedsubject matter, second pores 106 are formed between the zeoliteparticles 102. In an exemplary embodiment the second pores 106 have adiameter of about 1 to 10 micrometer, as indicated in FIG. 4. Due to thebinder, the individual particles 102 in FIG. 4 are adhered together toform a grain 108.

It should further be mentioned that although the zeolite particles 102are drawn with a rectangular shape in FIG. 4, the real zeolite particlesmay have a different form which depends on the actual structure of thezeolite particles.

FIG. 5 shows a plurality of grains 108 of the type shown in FIG. 4. Asindicated in FIG. 5, the diameter of the grains 108 is about 0.5 mm to0.6 mm in an embodiment.

By extensive experiments the inventors found that good sorbingcharacteristics can be obtained with a zeolite of the structure type FERor MFI. In the experiments it turned out that zeolites with a highsilicon to aluminium mass ratio are advantageous regarding theadsorption/desorption requirements. This may be due to an increasedhydrophobicity of these zeolites such that generally possible concurrentwater adsorption processes take place only to a limited extent.

Zeolite structures which can be synthesized in the form of pure SiO₂ oralmost pure SiO₂ are for example the types DDR, FER, MFI or BEA. Thethree letter code relates to the classification of zeolites according tothe International Zeolite Association and can be obtained inter aliafrom http://www.iza-online.org/. The code orders the zeolite accordingto their atomic structure. A zeolite in the form of at least pure SiO₂is characterized by a very low aluminium content, i.e. by a silicon toaluminium mass ratio over 200.

By extensive measurements it was found that the zeolite type FER has thehighest sorption capacity for nitrogen at room temperature among theinvestigated zeolites. Details of the experimental results are shown inFIG. 6 where the amount of adsorbed gas (nitrogen) A in millimol permilliliter (mmol/ml) is shown over the pressure p in millibar (mbar) forthe zeolite types BEA, MFI, FER and DDR. For measurement of theadsorption capacity, the pure silicon zeolites in powder form have beenactivated for 1 h at 500 degrees Celsius. Activation was performed toremove any possible residuals from the zeolite. The volume of zeolitewas determined by measuring the mass of the zeolite and dividing themass by the cristallographically determined density of the zeolite whichis also known to the skilled person.

To determine the aging behaviour of the investigated zeolites, nitrogenadsorption isotherms (amount of adsorbed gas A in mmol/ml over pressurep in mbar) have been determined after activation (curve 1) and afteraging for one week at ambient air under normal conditions (curve 2).

The results are shown in FIG. 7 for the zeolite type BEA, in FIG. 8 forthe zeolite type MFI and in FIG. 9 for the zeolite type FER.

To summarize the above findings, among the zeolites under considerationin pure SiO₂ modification, the structure type ferrierit (FER) has thehighest sorption capacity for nitrogen per volume unit at normalpressure and, in contrast to the zeolite type BEA in its almost pureSiO₂ modification, does not age. Up to now there is no explanation forthis surprising experimental result. Although it is known to the skilledperson that zeolites can adsorb different substances and that adsorptionof substances of high vapour pressure can lead to an obstruction of thepores and hence to a reduction of the sorption capacity of smallmolecules, it is not clear why the substances which are adsorbed byzeolite BEA apparently lead to an irreversible reduction of the sorptioncapacity and why this effect does not occur with the zeolite FER. Withthe zeolite type MFI only negligible aging processes occur due toenvironmental influences which lead to a likewise negligible reductionof the sorption capacity in the loudspeaker device. Hence, the zeoliteMFI in its aging behaviour is comparable to the zeolite type FER.

Hence, zeolite type FER is a promising candidate for the application asa sorber material in a loudspeaker device in accordance with the hereindisclosed subject-matter. However, it should be understood that alsoother types of zeolites can be used for providing a zeolite materialaccording to the herein disclosed subject matter.

In a comparison of the pore diameters of the intrinsic pores of thezeolites under investigation, it was found that the diameters of theintrinsic pores of the zeolites BEA, MFI, FER, DDR fall continuously inthe order from 0.7 nm to 0.4 nm. From the experiments it appearsadvantageous to use zeolites with a small intrinsic pore diameter,wherein the lower boundary for the intrinsic pore diameter is given bythe size of the nitrogen molecule which is about 0.4 nm. However, up tonow there is no explanation for the bad performance of the DDR zeolitewith the pore diameter of 0.44 nm×0.36 nm which should provide a goodaccessibility for nitrogen.

Generally it is possible that other zeolite types which can be producedin a hydrophobic form are as well suitable for providing a zeolitematerial according to the herein disclosed subject matter. For example,the zeolite types CHA, IHW, IWV, ITE, UTL, VET, MTW can also be producedas pure or doped SiO₂ modifications and have hydrophobic properties.Doping can be performed with, for example, elements of the fourth groupof the periodic table, e.g. with germanium.

From the experiments it was found that the particle size of the primaryparticles of the zeolite is advantageously below 10 μm. According to anembodiment of the herein disclosed subject-matter, the diameter of theprimary particles is below 5 μm. According to a further embodiment, thediameter of the primary particles is below 2 μm. According to a furtherembodiment, the diameter of the primary particles is larger than 300 nm.

It was shown by comparison measurements that a diameter of the primaryparticles larger than 10 μm is detrimental for the enlargement of thevirtual acoustic volume of the resonance space of the loudspeakerdevice. FIG. 10 exemplarily shows measurements of the electric impedanceI in Ohm (Ω) over frequency f in Hertz (Hz) of a loudspeaker device withFER zeolite in powder application with different diameters of theprimary particles. To this end, the electric impedance curves of aloudspeaker device with an empty resonance space and with the resonancespace filled with FER zeolite in pure SiO₂ modification was measured fortwo different particles sizes. The applied mass of zeolite was 60 mg ineach case. The results are shown in FIG. 10. Curve (1) shows theimpedance of the loudspeaker device with FER zeolite with a diameter of5 μm. Curve (2) of FIG. 10 corresponds to the empty resonance space andcurve (3) corresponds to the resonance space filled with FER zeoliteswith a diameter of the primary particles of about 100 μm. Since thezeolite was applied in powder form no more zeolite could be applied inthe resonance space of the loudspeaker without considerable damping.From FIG. 10 it can be taken that for the primary particle diameter of100 μm the obtained shift of the resonance maximum compared to the emptyresonance space is lower than the shift of the resonance maximum for adiameter of the primary particles of 10 μm. Further, the full width athalf maximum of the resonance peak is much larger for the larger primaryparticle size.

From the experiments performed by the inventors it was found that for inpresence of macropores with a pore diameter of larger than the intrinsicmicropores of the zeolite the shift of the resonance peak is furtherincreased and the damping is reduced compared to the same materialwithout macropores. One experimental example (referred to hereinafter asa first method) how a large amount of these macropores can be obtainedis to use 44 g calcinated zeolite MFI in pure SiO₂ modification and witha primary particle size of 1 μm (diameter) and disperse this zeolite in96% ethanol. Then, a polyacrylate suspension is provided in an amountsuch that the concentration of the polyacrylate in the solid product is5%. To this end, an initial, aqueous polyacrylate suspension wasprovided with a concentration of 11 weight % polyacrylate. Thepolyacrylate suspension at first has been doubled in its volume with 96%ethanol and has been then added to the zeolite suspension underextensive stirring. The resultant mixture was poured onto a plate ofsize 50×50 cm² and a temperature of 160 degrees Celsius within 3-4seconds. The resultant solid was then broken up with a cutting mill andfractionated with analysis sieves. Of the thus obtained solid acumulative pore distribution was determined by mercury porosimetry. Theresult is shown in FIG. 11, curve (1), where the cumulative pore volumeVp in cubic millimeter per gram (mm³/g) is plotted over the porediameter d in micrometer (μm). It should be noted that the cumulativepore volume means that the volume level is constant if no pore volume ispresent at a specific pore diameter. Hence a pore diameter distributioncan be obtained from the first derivative of the cumulative pore volume(d(Vp)/d(d)).

Further, results of a comparison material according to embodiments ofthe herein disclosed subject matter are also shown in FIG. 11. Thecomparison material has been obtained from dispensing 44 g calcinatedzeolite MFI in pure SiO₂ modification and a primary particle size of 1μm in water. Subsequently, an aqueous polyacrylate suspension (11 weight% polyacrylate) was added such that a polymer portion related to thewhole solid content was 5%. The mixture was homogenized with a stirringdevice and was dried under stirring with hot air. The resultant solidwas broken with a cutting mill and fractionated with analysis sieves.The cumulative pore volume over pore diameter of this material which wasalso obtained by mercury porosimetry is shown as curve (2) in FIG. 11.From FIG. 11 it is apparent that the first method for preparation of thezeolite material leads to a considerable increase of the fraction ofmacropores with a diameter in the range of 1 μm-10 μm.

FIG. 12 shows the electric impedance (I) measurements of both materialsover frequency f, wherein curve (1) corresponds to the material withincreased macropore fraction, curve (2) corresponds to the comparisonmaterial and curve (3) corresponds to the empty resonance space. Thematerial with the increased macropore fraction leads to a higherresonance shift, a higher increase of the virtual acoustic volume, and,at the same time, to reduced damping.

In FIG. 13 sound pressure level (SPL) over frequency f measurements areshown for a commercially available micro-loudspeaker device type NXPRA11×15×3.5, the back volume (resonance space) of which amounts to 1cm². Line 1 shows the frequency response of the loudspeaker device withempty resonance space, line 2 shows the frequency response of thisloudspeaker device with activated carbon fibre web in the resonancespace and line 3 shows the frequency response of the same loudspeakerdevice with the zeolite material with increased macropore fraction inthe resonance space. The resonance frequency shifts to the same extentby both materials, the activated carbon fibre web and the zeolitematerial with the increased macropore fraction, from 800 Hz down to 630Hz. Also the damping of the two materials is comparable. Both materialsare damping the loudspeaker to such a weak extent that the originalsound pressure level of about 90 dB is maintained. However, the zeolitematerial with the increased macropore fraction is an electricallynon-conducting material and is not subjected to aging.

According to an embodiment, the individual constituents of the zeolitematerial, referred to as grains herein, have a diameter between 0.1 mmand 0.9 mm and include a plurality of zeolite particles (see FIG. 4 andFIG. 5 above). According to a further embodiment, the grains have adiameter in the range of 0.4 mm and 0.7 mm. For example, the abovereferenced zeolite material with increased macropore fraction has agrain size of 0.3 mm. For investigating the influence of the grain size,different grain size fractions have been taken with respective sievesand electrical impedance spectra of these materials have been taken.FIG. 14 shows the measured spectra (impedance I in Ohm over frequency fin Hertz). The respective grain diameters for the individual curves inFIG. 14 are given in mm. As is apparent from FIG. 14, for a graindiameter of 0.6 mm as well as below a grain diameter of 0.3 mm, thefrequency shift of the resonance maximum is smaller and the damping ishigher as for grain diameters in a range of 0.3 mm to 0.6 mm.

A grain size below 0.1 mm results in an undesirable movement of thegrains in the loudspeaker which may result in non-linear distortions ofthe sound. For grain diameters larger than 0.9 mm the acousticresistance undesirably increases.

According to a further embodiment of the herein disclosedsubject-matter, the sorber material contains less than 20% binder(polymer material). According to a further embodiment, the sorbermaterial contains less than 10% binder. According to a furtherembodiment, the sorber material contains at least 1% binder. The binderglues the zeolite primary particles together. It has turned out in theexperiments that for polymer fractions larger than 10% (in thesolid-state), the virtual acoustic volume enlargement that is achievedby introducing the material in the resonance space of the loudspeakerdevice is below 1.5. For polymer concentrations below 4% (again relatedto the whole mass in the solid-state (mass of polymer/whole mass)), theresulting material is instable and shows heavy abrasion. FIG. 15 showselectrical impedance (I) curves of materials with different polymerconcentrations over frequency f. The materials used for the spectra inFIG. 15 include zeolite particles of the zeolite with the increasedmacropore fraction obtained as described above (curve 1 in FIG. 11).Curve 1 of FIG. 15 is obtained for the zeolite material with 6% polymerand curve 2 of FIG. 15 is obtained for the zeolite material with 12%polymer. As is apparent from FIG. 15, the higher polymer content leadsto a smaller shift of the resonance frequency towards lower frequencies.

FIG. 16 shows a loudspeaker device 200 in accordance with embodiments ofthe herein disclosed subject matter. The loudspeaker device 200comprises a loudspeaker receptacle 202 for receiving a loudspeaker 3.Further, the loudspeaker device 200 comprises a zeolite material 100according to aspects and embodiments of the herein disclosed subjectmatter in a region 204, e.g. a resonance space, that is exposed to soundgenerated by the loudspeaker 3 of the loudspeaker device 200.

It should be noted that the term “comprising” does not exclude otherelements or steps and the “a” or “an” does not exclude a plurality. Alsoelements described in association with different embodiments may becombined. It should also be noted that reference signs in the claimsshould not be construed as limiting the scope of the claims.

In order to recapitulate the above described embodiments of the presentinvention one can state:

A loudspeaker device is presented which includes a zeolite materialcomprising zeolite particles having a silicon to aluminum mass ratio ofat least 200. For an increased pore fraction of pores with a diameter ina range between 0.7 micrometer and 30 micrometer shows an increasedshift of the resonance frequency down to lower frequencies has beenobserved.

LIST OF REFERENCE SIGNS

-   -   2 signal source    -   4 sealing    -   3 loudspeaker    -   5 closed volume    -   6 audio output port    -   7 soundcard    -   8 left line input port    -   9 right line input port    -   10 resistance    -   11 left output port    -   12 soundcard    -   14 left input    -   15 microphone    -   30 impedance measuring circuit    -   40 impedance response measuring circuit    -   50 setup for sound pressure level measurement    -   100 zeolite material    -   102 zeolite particle    -   104 first pore within zeolite particle    -   106 second pore between zeolite particles    -   108 grain    -   200 loudspeaker device    -   202 loudspeaker receptacle

What is claimed is:
 1. A zeolite granule for a back volume of anacoustic device, the zeolite granule comprising: a plurality of zeoliteparticles, each comprising silicon dioxide and aluminum constituents,and wherein the silicon to aluminum mass ratio is at least 200; and abinder agent that adheres the plurality of zeolite particles togetherinto the zeolite granule; wherein the zeolite granule has a diameterthat is less than 0.9 millimeters and is greater than 0.1 millimeters;and wherein the zeolite granule is adapted to shift a resonant frequencyof the back volume of the acoustic device and to reduce the electricalimpedance of the acoustic device.
 2. The zeolite granule according toclaim 1, wherein the zeolite granule comprises zeolite particles havinga mean diameter less than or equal to 10 micrometers.
 3. The zeolitegranule according to claim 1, wherein the zeolite granule compriseszeolite particles having a mean diameter greater than or equal to 0.1micrometers.
 4. The zeolite granule according to claim 1, wherein thezeolite granule comprises zeolite particles having a plurality ofmicropores, and the micropores have pore diameters between 0.4nanometers and 0.7 nanometers.
 5. The zeolite granule according to claim1, wherein the zeolite granule comprises zeolite particles having thestructure FER.
 6. The zeolite granule according to claim 1, wherein thezeolite granule comprises zeolite particles having the structure MFI. 7.The acoustic element according to claim 1, wherein the zeolite granulecomprises zeolite particles having the structure MFI and the structureFER.
 8. The zeolite granule according to claim 1, wherein the zeolitegranule comprises zeolite particles having one of the structures CHA,IHW, IWV, ITE, UTL, VET, or MTW.
 9. The zeolite granule according toclaim 1, wherein the zeolite granule comprises zeolite particles thatare hydrophobic.
 10. The zeolite granule according to claim 1, whereinthe zeolite granule comprises zeolite particles that are electricallyinsulating, and non-corrosive to metal.
 11. The zeolite granuleaccording to claim 1, wherein the zeolite granule comprises zeoliteparticles having a plurality of micropores, and the micropores have amean diameter in a first diameter range; wherein the zeolite granulecomprises a plurality of macropores disposed between the zeoliteparticles, wherein the macropores have a mean diameter in a seconddiameter range; and wherein the second diameter range is greater than orequal to the first diameter range by at least one order of magnitude.12. The zeolite granule according to claim 11, wherein the firstdiameter range is between 0.4 nanometers and 0.7 nanometers.
 13. Thezeolite granule according to claim 11, wherein the second diameter rangeis greater than or equal to 50 nanometers.
 14. The zeolite granuleaccording to claim 11, wherein the macropores have a pore diameterdistribution with a local peak in a diameter range between 0.7micrometers and 30 micrometers.
 15. The zeolite granule according toclaim 1, wherein the relation of the whole mass of the binder agent ofthe zeolite granule to the whole mass of the zeolite granule is in therange from 1% to 20%.
 16. The zeolite granule according to claim 1,wherein the binder agent is a polymer material.
 17. The zeolite granuleaccording to claim 1, wherein the binder agent is formed from apolyacrylate suspension, a polystyrolacetate suspension, apolyvinylacetate suspension, a polyethylvinylacetate suspension, or apolybutadien rubber suspension.
 18. An acoustic transducer housingcomprising: a frame defining an interior volume; and a port in theacoustic transducer housing configured for mounting an acoustictransducer, wherein a first portion of the interior volume of theacoustic transducer housing is a back volume, and wherein a secondportion of the interior volume of the acoustic transducer housing isconfigured to facilitate acoustic communication between the port and theback volume; and a predetermined amount of zeolite granules according toclaim 1 disposed within the back volume of the acoustic transducerhousing.
 19. An acoustic transducer device comprising: an acoustictransducer housing according to claim 18; and an acoustic transducermounted in the port of the acoustic transducer housing.
 20. An acousticelement for adsorbing and desorbing a gas medium contained within asubstantially closed volume of an acoustic device, the acoustic elementcomprising a plurality of zeolite grains, wherein each of the zeolitegrains is comprised of: a plurality of zeolite particles each comprisingsilicon and aluminum constituents, wherein the silicon to aluminum massratio of the particle is at least 200; and a polymer material that bindsthe plurality of zeolite particles together; wherein a plurality of thezeolite grains have a mean diameter that is less than 0.9 millimetersand greater than 0.1 millimeters; and wherein the zeolite grains areadapted to shift a resonant frequency of the substantially closed volumeand to reduce the electrical impedance of the acoustic device.
 21. Theacoustic element according to claim 20, wherein the zeolite grainscomprise zeolite particles that have the FER structure, the MFIstructure, or both the FER and MFI structures.
 22. The acoustic elementaccording to claim 20, wherein the zeolite grains comprise zeoliteparticles that have a mean diameter that is less than 10 micrometers andis greater than 0.1 micrometers.
 23. The acoustic element according toclaim 20, wherein the zeolite grains comprise zeolite particles that arehydrophobic, are electrically insulating, and are non-corrosive.
 24. Theacoustic element according to claim 20, wherein the zeolite grainscomprise zeolite particles that have a plurality of micropores, whereinthe micropores have a mean diameter in a first diameter range; wherein aportion of the zeolite grains each have a plurality of macroporesdisposed between the zeolite particles, wherein the macropores have amean diameter in a second diameter range; and wherein the seconddiameter range is greater than or equal to the first diameter range byat least one order of magnitude.
 25. The acoustic element according toclaim 24, wherein the first diameter range is between 0.4 nanometers and0.7 nanometers.
 26. The acoustic element according to claim 24, whereinthe second diameter range is greater than or equal to 50 nanometers. 27.The acoustic element according to claim 24, wherein the macropores havea pore diameter distribution with a local peak in a diameter rangebetween 0.7 micrometers and 30 micrometers.
 28. The acoustic elementaccording to claim 20, wherein the relation of the whole mass of thepolymer material of a zeolite grain to the whole mass of a zeolite grainis in the range from 1% to 20%.
 29. The acoustic element according toclaim 20, wherein the polymer material is formed from a polyacrylatesuspension, a polystyrolacetate suspension, a polyvinylacetatesuspension, a polyethylvinylacetate suspension, or a polybutadien rubbersuspension.
 30. The acoustic element according to claim 20, wherein thezeolite grains have a high sorption capacity for nitrogen gas and a highsorption coefficient at approximately one atmosphere of pressure. 31.The acoustic element according to claim 20, wherein the zeolite grainsdo not undergo a substantial degradation of sorption capacity fornitrogen gas in the fluid medium on a per volume unit basis at oneatmosphere of pressure.
 32. A loudspeaker housing comprising: athree-dimensional enclosure that defines an acoustic chamber; and anaperture in the loudspeaker housing configured for coupling aloudspeaker to the acoustic chamber, wherein a first section of theacoustic chamber of the loudspeaker housing is a back volume, andwherein a second section of the acoustic chamber of the loudspeakerhousing is configured to acoustically couple the aperture and the backvolume; and an acoustic element according to claim 20 disposed withinthe back volume of the loudspeaker housing.
 33. An acoustic devicecomprising: a loudspeaker housing according to claim 32; and aloudspeaker mounted in the receptacle of the loudspeaker housing,wherein portion of the loudspeaker is disposed within thethree-dimensional enclosure and is acoustically coupled to the backvolume and the acoustic element via the second section of the acousticchamber.
 34. A zeolite sound adsorber for adsorbing and desorbing a gasmedium contained within a substantially closed volume of an acousticdevice, the zeolite sound adsorber comprising a plurality of zeolitegrains, wherein each of the zeolite grains is comprised of: a pluralityof zeolite particles each comprising silicon and aluminum constituentsin a predetermined silicon to aluminum mass ratio; and a polymermaterial that binds the plurality of zeolite particles together; whereinthe zeolite sound adsorber is hydrophobic, non-corrosive, andelectrically insulating; and wherein the zeolite sound adsorber isadapted to shift a resonant frequency of the substantially closed volumeand to reduce the electrical impedance of the acoustic device.
 35. Thezeolite sound adsorber according to claim 34, wherein the predeterminedsilicon to aluminum mass ratio is at least
 200. 36. The zeolite soundadsorber according to claim 34, wherein the predetermined silicon toaluminum mass ratio is at least
 300. 37. The zeolite sound adsorberaccording to claim 34, wherein the zeolite grains comprise zeoliteparticles having the structure FER.
 38. The zeolite sound adsorberaccording to claim 34, wherein the zeolite grains comprise zeoliteparticles having the structure MFI.
 39. The zeolite sound adsorberaccording to claim 34, wherein the zeolite sound adsorber do not undergoa substantial degradation of sorption capacity for nitrogen gas on a pervolume unit basis at one atmosphere of pressure.
 40. The zeolite soundadsorber according to claim 34, wherein the zeolite sound adsorberchanges the acoustic compliance of the gas contained within thesubstantially closed volume.
 41. The zeolite sound adsorber according toclaim 34, wherein a plurality of the zeolite grains have a mean diameterthat is less than 0.9 millimeters and is greater than 0.1 millimeters.42. An acoustic device comprising: a loudspeaker housing comprising aback volume and a mounting port for a loudspeaker; a loudspeakerdisposed in the mounting port, wherein a portion of the loudspeaker isacoustically coupled to the back volume; and an acoustic elementdisposed in the back volume, wherein the acoustic element comprises azeolite sound adsorber according to claim 34.